Self-focusing of a Gaussian laser beam in parabolic profile optical fiber having Kerr non-linealrity

Abstract

A steady state analysis of self-focusing of Gaussian laser beam propagating in a parabolic index profile silica fiber of cylindrical core has been presented. The Kerr non-linearity acts as perturbation on the geometrically built-in radial inhomogeneity of the dielectric fiber. A paraxial ray approach has been adopted following Akhmanov and Sodha using WKB approximation. The beam-width parameter at different axial points is studied by varying different parameters. An appreciable decrease in critical beam power for focusing has been reported. It has been found that when the beam power attains this threshold value, the beam propagates in a self-trapped waveguide mode. Above the threshold, the beam gets self-focused when the non-linear effect dominates over the diffraction effect. Below this threshold the beam diverges out forming a diverging lens. The beam intensity at the focusing points has been calculated for the fiber for different media and fiber lasers. The propagation characteristics of laser beam arc found to be very sensitive with respect to the delta parameter

of the fiber and the self-focusing length is found to decrease with the increase in incident beam power. Results indicate the possibility of a new kind of passive non-linear optical device for manipulating output light intensity.